1. Field of the Invention
The present invention relates generally to the field of audio amplification, especially for hearing aids. More particularly, the invention provides a method for efficiently cancelling acoustic feedback in the hearing aid.
2. Prior Art
Acoustic feedback in a hearing aid, from the electroacoustic transducer (commonly referred to as the “receiver”) back to the microphone, is common and difficult to suppress. Feedback may produce an audible whistle, which is irritating to the hearing aid wearer so that the wearer must often reduce the volume to a lower than desired level, thereby reducing the effectiveness of the hearing aid.
One reason that it is difficult to effectively suppress acoustic feedback in a hearing aid is that the frequency at which feedback occurs varies with changing external conditions. Therefore, for feedback to be effectively cancelled without undesirably degrading the amplified signal, some form of adaptive cancellation is required. Various techniques have been proposed for implementing adaptive feedback cancellation. Such techniques are disclosed, for example, in U.S. Pat. Nos. 5,016,280; 5,091,952 and 5,259,033.
One of the principal design objectives for hearing aids is miniaturization of physical volume. Most wearers prefer a hearing aid that can be worn entirely within the ear. Advances in microelectronics have vastly improved the signal processing capabilities of in-the-ear (ITE) hearing aids. Even so, the provision of effective feedback cancellation remains a practical design challenge. Prior art techniques necessarily require certain trade-offs. As a result of such trade-offs, the hearing aid may exhibit only a small increase in maximum stable gain, slow filter adaptation, distortion, interference and/or lack of adaptation to individual wearers.